EVANSDALE, Iowa — Investigators reclassified the disappearance of two missing Iowa cousins as an abduction case Friday after an FBI dive team failed to find their bodies in a lake near where they were last seen a week ago.

Lyric Cook-Morrissey, 10, and Elizabeth Collins, 8, vanished after riding bikes near Meyers Lake in Evansdale, a small town in northeast Iowa that has been devastated by their disappearance. Their bikes were later found on a path near the lake.

Investigators are confident the girls did not drown or die in the lake, and they do not believe the girls got lost because they would have been found by now, Black Hawk County Chief Deputy Rick Abben told reporters during an afternoon news briefing.

"Since we can't find them, and they are not in the lake, we're calling it an abduction," said Abben, who announced a $50,000 reward for information leading to an arrest and conviction. "Now that it's an abduction, everyone is a suspect until we find these people, these two young girls."

Abben spoke after an FBI dive team that focuses on underwater searches spent hours Friday on a boat equipped with sonar equipment, searching the bottom of the 26-acre lake. FBI spokeswoman Sandy Breault said divers were confident the girls were not there based on the surveillance, and they did not need to conduct any dives. The lake had been partially drained, and the sandy and muddy bottom could be seen in some spots.

The shift in the case also came after authorities took steps to keep a closer watch on Lyric's father, a man with a lengthy criminal history who has stopped cooperating with police.

A judge on Thursday granted a prosecution request to place Daniel Morrissey, 36, in a pretrial supervision program of the Iowa Department of Corrections while he faces September trials in two separate drug cases that could land him in prison for decades. The change means Morrissey, who has been free on bond, will be supervised by parole officers who will make sure he shows up in court and does not violate the terms of his release.

Abben said authorities sought the order "so that we have a little bit closer" monitoring of Morrissey. But he also said Morrissey was not considered a suspect, and investigators were scrutinizing others in the family with criminal histories.

"We're looking at everybody, not just one set of parents over the other. Not just because one family may have a criminal background. Everything has to be considered," Abben said.

Morrissey's wife, Misty Cook-Morrissey, 34, pleaded guilty in 2003 in federal court to conspiracy to manufacture and distribute methamphetamine, court documents show. She also has theft and alcohol violations in state court and is on supervised release after her probation was revoked in September because of drug and excessive alcohol use and failure to comply with drug tests.

Cook-Morrissey, told KWWL-TV on Friday that she believed authorities were unfairly scrutinizing her and her husband because of their criminal histories. She said she believed police were getting frustrated after searching extensively for a week and coming up empty.

"It's frustrating for us as well," she said.

Black Hawk County prosecutor Brad Walz said Morrissey should have been placed under supervision when he was released on bond in May. Morrissey faces five charges that each carry 45-year prison terms, including possession of methamphetamine with intent to deliver and conspiracy to manufacture methamphetamine.

Messages left for Morrissey's defense lawyer Friday were not returned.

With the search of the lake complete, Abben said city officials will halt their efforts to drain the body of water. They started the process earlier in the week and then stopped it Thursday because the FBI's special equipment needed a certain amount of water to work.

Abben said investigators will continue to chase leads through the weekend. They have sent some evidence to the Iowa Division of Criminal Investigation laboratory in Ankeny for analysis, he said, although he would not elaborate on what it was.

Police conducted checkpoints throughout Evansdale on Friday, but Abben didn't say whether those had yielded the evidence. He did say no weapons were found.

The working-class community of 4,700 near Waterloo has rallied to show support for the girls. Many residents have been wearing T-shirts bearing the cousins' pictures and posted hand-written notes to them at the lake. They planned to release balloons at a local park Friday evening, and a benefit run for the girls' families was scheduled for Saturday morning in Waterloo.

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Associated Press writer David Pitt in Des Moines contributed to this report.